3d micro display semiconductor device and structure

ABSTRACT

A 3D micro display, the 3D micro display including: a first level including a first single crystal layer, the first single crystal layer includes at least one LED driving circuit; a second level including a first plurality of light emitting diodes (LEDs), the first plurality of LEDs including a second single crystal layer, where the second level is disposed on top of the first level, where the second level includes at least ten individual first LED pixels; and a bonding structure, where the bonding structure includes oxide to oxide bonding.

CROSS-REFERENCE OF RELATED APPLICATION

This application claims priority of and is a continuation of U.S. patentapplication Ser. No. 17/487,369 filed on Sep. 28, 2021; which is acontinuation of U.S. patent application Ser. No. 17/216,597 filed onMar. 29, 2021, now U.S. Pat. No. 11,164,898 issued on Nov. 2, 2021;which is a continuation-in-part of U.S. patent application Ser. No.17/113,045 filed on Dec. 5, 2020, now U.S. Pat. No. 10,998,374 issued onMay 4, 2021; which is a continuation-in-part of U.S. patent applicationSer. No. 17/027,217 filed on Sep. 21, 2020; which is acontinuation-in-part of U.S. patent application Ser. No. 16/860,027filed on Apr. 27, 2020, now U.S. Pat. No. 10,833,108 issued on Nov. 10,2020; which is a continuation-in-part of U.S. patent application Ser.No. 15/920,499 filed on Mar. 14, 2018, now U.S. Pat. No. 10,679,977issued on Jun. 9, 2020; which is a continuation-in-part of U.S. patentapplication Ser. No. 14/936,657 filed on Nov. 9, 2015, now U.S. Pat. No.9,941,319 issued on Apr. 10, 2018; which is a continuation-in-part ofU.S. patent application Ser. No. 13/274,161 filed on Oct. 14, 2011, nowU.S. Pat. No. 9,197,804 issued on Nov. 24, 2015; and this application isa continuation-in-part of U.S. patent application Ser. No. 12/904,103filed on Oct. 13, 2010, now U.S. Pat. No. 8,163,581 issued on Apr. 24,2012.

BACKGROUND OF THE INVENTION (A) Field of the Invention

This invention describes applications of monolithic 3D integration tovarious disciplines, including but not limited to, for example,light-emitting diodes and displays.

(B) Discussion of Background Art

Semiconductor and optoelectronic devices often require thinmonocrystalline (or single-crystal) films deposited on a certain wafer.To enable this deposition, many techniques, generally referred to aslayer transfer technologies, have been developed. These include:

-   -   Ion-cut, variations of which are referred to as smart-cut,        nano-cleave and smart-cleave: Further information on ion-cut        technology is given in “Frontiers of silicon-on-insulator,” J.        Appl. Phys. 93, 4955-4978 (2003) by G. K. Celler and S.        Cristolovean (“Celler”) and also in “Mechanically induced Si        layer transfer in hydrogen-implanted Si wafers,” Appl. Phys.        Lett., vol. 76, pp. 2370-2372, 2000 by K. Henttinen, I. Suni,        and S. S. Lau (“Hentinnen”).    -   Porous silicon approaches such as ELTRAN: These are described in        “Eltran, Novel SOI Wafer Technology”, JSAP International, Number        4, July 2001 by T. Yonehara and K. Sakaguchi (“Yonehara”).    -   Lift-off with a temporary substrate, also referred to as        epitaxial lift-off: This is described in “Epitaxial lift-off and        its applications”, 1993 Semicond. Sci. Technol. 8 1124 by P.        Demeester, et al (“Demeester”).    -   Bonding a substrate with single crystal layers followed by        Polishing, Time-controlled etch-back or Etch-stop layer        controlled etch-back to thin the bonded substrate: These are        described in U.S. Pat. No. 6,806,171 by A. Ulyashin and A.        Usenko (“Ulyashin”) and “Enabling SOI-Based Assembly Technology        for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDM        Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L.        Shi, S. M. Alam, D. J. Frank, S. E. Steen, J. Vichiconti, D.        Posillico, M. Cobb, S. Medd, J. Patel, S. Goma, D.        DiMilia, M. T. Robson, E. Duch, M. Farinelli, C. Wang, R. A.        Conti, D. M. Canaperi, L. Deligianni, A. Kumar, K. T.        Kwietniak, C. D'Emic, J. Ott, A. M. Young, K. W. Guarini, and M.        Ieong (“Topol”).    -   Bonding a wafer with a Gallium Nitride film epitaxially grown on        a sapphire substrate followed by laser lift-off for removing the        transparent sapphire substrate: This method may be suitable for        deposition of Gallium Nitride thin films, and is described in        U.S. Pat. No. 6,071,795 by Nathan W. Cheung, Timothy D. Sands        and William S. Wong (“Cheung”).    -   Rubber stamp layer transfer: This is described in “Solar cells        sliced and diced”, 19 May 2010, Nature News.

With novel applications of these methods and recognition of theirindividual strengths and weaknesses, one can significantly enhancetoday's light-emitting diode (LED), display, image-sensor and solar celltechnologies.

Background on LEDs

Light emitting diodes (LEDs) are used in many applications, includingautomotive lighting, incandescent bulb replacements, and as backlightsfor displays. Red LEDs are typically made on Gallium Arsenide (GaAs)substrates, and include quantum wells constructed of various materialssuch as AlInGaP and GaInP. Blue and green LEDs are typically made onSapphire or Silicon Carbide (SiC) or bulk Gallium Nitride (GaN)substrates, and include quantum wells constructed of various materialssuch as GaN and InGaN.

A white LED for lighting and display applications can be constructed byeither using a blue LED coated with phosphor (called phosphor-coated LEDor pcLED) or by combining light from red, blue, and green LEDs (calledRGB LED). RGB LEDs are typically constructed by placing red, blue, andgreen LEDs side-by-side. While RGB LEDs are more energy-efficient thanpcLEDs, they are less efficient in mixing red, blue and green colors toform white light. They also are much more costly than pcLEDs. To tackleissues with RGB LEDs, several proposals have been made.

One RGB LED proposal from Hong Kong University is described in “Designof vertically stacked polychromatic light emitting diodes”, OpticsExpress, June 2009 by K. Hui, X. Wang, et al (“Hui”). It involvesstacking red, blue, and green LEDs on top of each other afterindividually packaging each of these LEDs. While this solves lightmixing problems, this RGB-LED is still much more costly than a pcLEDsolution since three LEDs for red, blue, and green color need to bepackaged. A pcLED, on the other hand, requires just one LED to bepackaged and coated with phosphor.

Another RGB LED proposal from Nichia Corporation is described in“Phosphor Free High-Luminous-Efficiency White Light-Emitting DiodesComposed of InGaN Multi-Quantum Well”, Japanese Journal of AppliedPhysics, 2002 by M. Yamada, Y. Narukawa, et al. (“Yamada”). It involvesconstructing and stacking red, blue and green LEDs of GaN-basedmaterials on a sapphire or SiC substrate. However, red LEDs are notefficient when constructed with GaN-based material systems, and thathampers usefulness of this implementation. It is not possible to depositdefect-free AlInGaP/InGaP for red LEDs on the same substrate as GaNbased blue and green LEDs, due to a mismatch in thermal expansionco-efficient between the various material systems.

Yet another RGB-LED proposal is described in “Cascade Single chipphosphor-free while light emitting diodes”, Applied Physics Letters,2008 by X. Guo, G. Shen, et al. (“Guo”). It involves bonding GaAs basedred LEDs with GaN based blue-green LEDs to produce white light.Unfortunately, this bonding process requires 600° C. temperatures,causing issues with mismatch of thermal expansion co-efficients andcracking. Another publication on this topic is “A trichromaticphosphor-free white light-emitting diode by using adhesive bondingscheme”, Proc. SPIE, Vol. 7635, 2009 by D. Chuai, X. Guo, et al.(“Chuai”). It involves bonding red LEDs with green-blue LED stacks.Bonding is done at the die level after dicing, which is more costly thana wafer-based approach.

U.S. patent application Ser. No. 12/130,824 describes various stackedRGB LED devices. It also briefly mentions a method for construction of astacked LED where all layers of the stacked LED are transferred usinglift-off with a temporary carrier and Indium Tin Oxide (ITO) tosemiconductor bonding. This method has several issues for constructing aRGB LED stack. First, it is difficult to manufacture a lift-off with atemporary carrier of red LEDs for producing a RGB LED stack, especiallyfor substrates larger than 2 inch. This is because red LEDs aretypically constructed on non-transparent GaAs substrates, and lift-offwith a temporary carrier is done by using an epitaxial lift-off process.Here, the thin film to be transferred typically sits atop a“release-layer” (eg. AlAs), this release layer is removed by etchprocedures after the thin film is attached to a temporary substrate.Scaling this process to 4 inch wafers and bigger is difficult. Second,it is very difficult to perform the bonding of ITO to semiconductormaterials of a LED layer at reasonable temperatures, as described in thepatent application Ser. No. 12/130,824.

It is therefore clear that a better method for constructing RGB LEDswill be helpful. Since RGB LEDs are significantly more efficient thanpcLEDs, they can be used as replacements of today's phosphor-based LEDsfor many applications, provided a cheap and effective method ofconstructing RGB LEDs can be invented.

Background on Displays:

Liquid Crystal Displays (LCDs) can be classified into two types based onmanufacturing technology utilized: (1) Large-size displays that are madeof amorphous/polycrystalline silicon thin-film-transistors (TFTs), and(2) Microdisplays that utilize single-crystal silicon transistors.Microdisplays are typically used where very high resolution is needed,such as camera/camcorder view-finders, projectors and wearablecomputers.

Microdisplays are made in semiconductor fabs with 200 mm or 300 mmwafers. They are typically constructed with LCOS(Liquid-Crystal-on-Silicon) Technology and are reflective in nature. Anexception to this trend of reflective microdisplays is technology fromKopin Corporation (U.S. Pat. No. 5,317,236, filed December 1991). Thiscompany utilizes transmittive displays with a lift-off layer transferscheme. Transmittive displays may be generally preferred for variousapplications.

While lift-off layer transfer schemes are viable for transmittivedisplays, they are frequently not used for semiconductor manufacturingdue to yield issues. Therefore, other layer transfer schemes will behelpful. However, it is not easy to utilize other layer transfer schemesfor making transistors in microdisplays. For example, application of“smart-cut” layer transfer to attach monocrystalline silicon transistorsto glass is described in “Integration of Single Crystal Si TFTs andCircuits on a Large Glass Substrate”, IEDM 2009 by Y. Takafuji, Y.Fukushima, K. Tomiyasu, et al. (“Takafuji”). Unfortunately, hydrogen isimplanted through the gate oxide of transferred transistors in theprocess, and this degrades performance. Process temperatures are as highas 600° C. in this paper, and this requires costly glass substrates.Several challenges therefore need to be overcome for efficient layertransfer, and require innovation.

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplementaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate the performance, functionality and powerconsumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low.

There are many techniques to construct 3D stacked integrated circuits orchips including:

Through-silicon via (TSV) technology: Multiple layers of transistors(with or without wiring levels) can be constructed separately. Followingthis, they can be bonded to each other and connected to each other withthrough-silicon vias (TSVs).

SUMMARY

Techniques to utilize layer transfer schemes such as ion-cut to formnovel light emitting diodes (LEDs), displays, and microdisplays arediscussed.

In one aspect, a multi-level semiconductor device, the device including:a first level including integrated circuits; a second level, where thesecond level is disposed above the first level, where the first levelincludes crystalline silicon; and an oxide layer disposed between thefirst level and the second level, where the second level is bonded tothe oxide layer, and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer includesat least ten individual first LED pixels; and a second plurality oflight emitting diodes (LEDs), where the first plurality of lightemitting diodes (LEDs) emits a first light with a first wavelength,where the second plurality of light emitting diodes (LEDs) emits asecond light with a second wavelength, where the first wavelength andthe second wavelength differ by greater than 10 nm, and where the 3Dmicro display includes an oxide to oxide bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer is on topof the first single crystal layer, where the second single crystal layerincludes at least ten individual first LED pixels; and a secondplurality of light emitting diodes (LEDs), where the 3D micro displayincludes an oxide to oxide bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer includesat least ten individual first LED pixels; and a second plurality oflight emitting diodes (LEDs), where the first plurality of lightemitting diodes (LEDs) emits a first light with a first wavelength,where the second plurality of light emitting diodes (LEDs) emits asecond light with a second wavelength, where the first wavelength andthe second wavelength differ by greater than 10 nm, and where the 3Dmicro display includes an oxide to oxide bonding structure.

In another aspect, a light-emitting integrated wafer structure includesthree overlying layers, where each of the three overlying layers emitslight at a different wavelength and where at least one of the threeoverlying layers is transferred to the light-emitting integrated waferstructure using one of atomic species implants assisted cleaving, laserlift-off, etch-back, or chemical-mechanical-polishing (CMP).

In another aspect, an integrated image sensor includes two overlyinglayers, where one of the two overlying layers is an image sensor layerand at least one of the two overlying layers is less than 5 micronsthick, and where the two overlying layers are constructed at atemperature not exceeding 450° C.

In another aspect, a display device with junction-less transistors isdisclosed.

In yet another aspect, a method for fabricating a light-emittingintegrated device, includes overlying three layers, where each of thethree layers emits light at a different wavelength, and where theoverlying includes one of: performing an atomic species implantation,performing a laser lift-off, performing an etch-back, orchemical-mechanical polishing (CMP).

In another aspect, a method for fabricating an integrated image sensor,includes overlying a first layer on a second layer to form a combinedlayer, where one of the first and second layers is an image sensor layerand at least one of the first and second layers is less than 5 micronsthick, and where the overlying is performed at a temperature notexceeding 450° C.

In yet another aspect, a method is disclosed for forming a display whosepixels are controlled by junction-less transistors.

In another aspect, a method for enabling 3D viewing of objects in animage through actual physical distances of individual objects to theviewer displayed separately on a display screen actuated by a fastmotor.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including a first plurality of light emittingdiodes (LEDs), a second single crystal layer including a secondplurality of light emitting diodes (LEDs), where the first singlecrystal layer includes at least ten individual first LED pixels, wherethe second single crystal layer includes at least ten individual secondLED pixels, where the first plurality of light emitting diodes (LEDs)emits a first light with a first wavelength, where the second pluralityof light emitting diodes (LEDs) emits a second light with a secondwavelength, where the first wavelength and the second wavelength differby greater than 10 nm, and where the 3D micro display includes an oxideto oxide bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer is on topof the first single crystal layer, where the second single crystal layerincludes at least ten individual first LED pixels; and a secondplurality of light emitting diodes (LEDs), where the 3D micro displayincludes a bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer includesat least ten individual first LED pixels; and a second plurality oflight emitting diodes (LEDs), where the first plurality of lightemitting diodes (LEDs) emits a first light with a first wavelength,where the second plurality of light emitting diodes (LEDs) emits asecond light with a second wavelength, where the first wavelength andthe second wavelength differ by greater than 10 nm, and where the 3Dmicro display includes a bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including a first plurality of light emittingdiodes (LEDs); a second single crystal layer including a secondplurality of light emitting diodes (LEDs), where the first singlecrystal layer includes at least ten individual first LED pixels, wherethe second single crystal layer includes at least ten individual secondLED pixels, where the first plurality of light emitting diodes (LEDs)emits a first light with a first wavelength, where the second pluralityof light emitting diodes (LEDs) emits a second light with a secondwavelength, where the first wavelength and the second wavelength differby greater than 10 nm; and further including a third single crystallayer including at least one LED driving circuit.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including at least one LED driving circuit; asecond single crystal layer including a first plurality of lightemitting diodes (LEDs), where the second single crystal layer isdisposed on top of the first single crystal layer, where the secondsingle crystal layer includes at least ten individual first LED pixels,where the 3D micro display includes a bonding structure, and where thebonding structure includes oxide to oxide bonding.

In another aspect, a 3D micro display, the 3D micro display including: afirst single crystal layer including a plurality of LED drivingcircuits; a second single crystal layer including a first plurality oflight emitting diodes (LEDs), where the second single crystal layerincludes at least ten individual first LED pixels; and a secondplurality of light emitting diodes (LEDs), where the first plurality oflight emitting diodes (LEDs) emits a first light with a firstwavelength, where the second plurality of light emitting diodes (LEDs)emits a second light with a second wavelength, where the firstwavelength and the second wavelength differ by greater than 10 nm, wherethe plurality of LED driving circuit include individual control of eachof the first plurality of light emitting diodes (LEDs), and where the 3Dmicro display includes a bonding structure.

In another aspect, a 3D micro display, the 3D micro display including: afirst level comprising a first single crystal layer, said first singlecrystal layer comprises at least one LED driving circuit; a second levelcomprising a first plurality of light emitting diodes (LEDs), said firstplurality of LEDs comprising a second single crystal layer, wherein saidsecond level is disposed on top of said first level, wherein said secondlevel comprises at least ten individual first LED pixels; and a bondingstructure, wherein said bonding structure comprises oxide to oxidebonding.

In another aspect, a 3D micro display, the 3D micro display including: afirst level comprising a first single crystal layer, said first singlecrystal layer comprises at least one LED driving circuit; a second levelcomprising a first plurality of light emitting diodes (LEDs), said firstplurality of LEDs comprising a second single crystal layer, wherein saidsecond level is disposed on top of said first level, wherein said secondlevel comprises at least ten individual first LED pixels; and a bondingstructure, wherein said first level is bonded to said second level, andwherein said bonded comprises oxide to oxide bonding.

In another aspect, a 3D micro display, the 3D micro display including: afirst level comprising a first single crystal layer, said first singlecrystal layer comprises at least one LED driving circuit; a second levelcomprising a first plurality of light emitting diodes (LEDs), said firstplurality of LEDs comprising a second single crystal layer, wherein saidsecond level is disposed on top of said first level, wherein said secondlevel comprises at least ten individual first LED pixels, wherein saidfirst plurality of LEDs comprise at least 10 individual LED pixels,wherein said at least 10 individual LED pixels been made individual byan etch process; and a bonding structure, wherein said first level isbonded to said second level, and wherein said bonded comprises oxide tooxide bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIGS. 1A-1B illustrate red, green and blue type LEDs (prior art);

FIG. 2 illustrates a conventional RGB LED where red, green, and blueLEDs are placed side-by-side (prior art);

FIG. 3 illustrates a prior-art phosphor-based LED (pcLED);

FIGS. 4A-4S illustrate an embodiment of this invention, where RGB LEDsare stacked with ion-cut technology, flip-chip packaging and conductiveoxide bonding;

FIGS. 5A-5Q illustrate an embodiment of this invention, where RGB LEDsare stacked with ion-cut technology, wire bond packaging and conductiveoxide bonding;

FIGS. 6A-6L illustrate an embodiment of this invention, where stackedRGB LEDs are formed with ion-cut technology, flip-chip packaging andaligned bonding;

FIGS. 7A-7L illustrate an embodiment of this invention, where stackedRGB LEDs are formed with laser lift-off, substrate etch, flip-chippackaging and conductive oxide bonding;

FIGS. 8A-8B illustrate an embodiment of this invention, where stackedRGB LEDs are formed from a wafer having red LED layers and another waferhaving both green and blue LED layers;

FIG. 9 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits for the LED built onthe silicon sub-mount;

FIG. 10 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits as well as imagesensors for the LED built on the silicon sub-mount;

FIGS. 11A-11F is a prior art illustration of pcLEDs constructed withion-cut processes;

FIGS. 12A-12F illustrate an embodiment of this invention, where pcLEDsare constructed with ion-cut processes;

FIGS. 13A-13G are exemplary drawn illustrations of a display constructedusing sub-400° C. processed single crystal silicon recessed channeltransistors on a glass substrate;

FIGS. 14A-14H are exemplary drawn illustrations of a display constructedusing sub-400° C. processed single crystal silicon replacement gatetransistors on a glass substrate;

FIGS. 15A-15F are exemplary drawn illustrations of a display constructedusing sub-400° C. processed single crystal junction-less transistors ona glass substrate;

FIGS. 16A-16D are exemplary drawn illustrations of a display constructedusing sub-400° C. processed amorphous silicon or polysiliconjunction-less transistors on a glass substrate;

FIGS. 17A-17C are exemplary drawn illustrations of a microdisplayconstructed using stacked RGB LEDs and control circuits are connected toeach pixel with solder bumps;

FIGS. 18A-18D are exemplary drawn illustrations of a microdisplayconstructed using stacked RGB LEDs and control circuits aremonolithically stacked above the LED; and

FIGS. 19A-19D illustrate embodiments of this invention, where multiplescreens which may be actuated by motors are used to render displays in3D.

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference toFIGS. 1-19, it being appreciated that the figures illustrate the subjectmatter not to scale or to measure.

NuLED Technology:

FIG. 1A illustrates a cross-section of prior art red LEDs. Red LEDs aretypically constructed on a Gallium Arsenide substrate 100.Alternatively, Gallium Phosphide or some other material can be used forthe substrate. Since Gallium Arsenide 100 is opaque, a Bragg Reflector101 is added to ensure light moves in the upward direction. Red light isproduced by a p-n junction with multiple quantum wells (MQW). A p-typeconfinement layer 104, a n-type confinement layer 102 and a multiplequantum well 103 form this part of the device. A current spreadingregion 105 ensures current flows throughout the whole device and notjust close to the contacts. Indium Tin Oxide (ITO) could be used for thecurrent spreading region 105. A top contact 106 and a bottom contact 107are used for making connections to the LED. It will be obvious to oneskilled in the art based on the present disclosure that manyconfigurations and material combinations for making red LEDs arepossible. This invention is not limited to one particular configurationor set of materials.

FIG. 1B also illustrates green and blue LED cross-sections. These aretypically constructed on a sapphire, SiC or bulk-GaN substrate,indicated by 108. Light is produced by a p-n junction with multiplequantum wells made of InxGa1-xN/GaN. A p-type confinement layer 111, an-type confinement layer 109 and a multiple quantum well 110 form thispart of the device. The value of subscript x in InxGa1-xN determineswhether blue light or green light is produced. For example, blue lighttypically corresponds to x ranging from 10% to 20% while green lighttypically corresponds to x ranging from 20% to 30%. A current spreader112 is typically used as well. ITO could be a material used for thecurrent spreader 112. An alternative material for current spreadingcould be ZnO. A top contact 113 and a bottom contact 114 are used formaking connections to the LED. It will be obvious to one skilled in theart based on the present disclosure that many configurations andmaterial combinations for making blue and green LEDs are possible. Thisinvention is not limited to one particular configuration or set ofmaterials.

White LEDs for various applications can be constructed in two ways.Method 1 is described in FIG. 2 which shows Red LED 201, blue LED 202,and green LED 203 that are constructed separately and placedside-by-side. Red light 204, blue light 205 and green light 206 aremixed to form white light 207. While these “RGB LEDs” are efficient,they suffer from cost issues and have problems related to light mixing.Method 2 is described in FIG. 3 which shows a blue LED 301 constructedand coated with a phosphor layer 302. The yellow phosphor layer convertsblue light into white light 303. These “Phosphor-based LEDs” or “pcLEDs”are cheaper than RGB LEDs but are typically not as efficient.

FIG. 4A-S illustrate an embodiment of this invention where Red, Blue,and Green LEDs are stacked on top of each other with smart layertransfer techniques. A smart layer transfer may be defined as one ormore of the following processes:

-   -   Ion-cut, variations of which are referred to as smart-cut,        nano-cleave and smart-cleave: Further information on ion-cut        technology is given in “Frontiers of silicon-on-insulator,” J.        Appl. Phys. 93, 4955-4978 (2003) by G. K. Celler and S.        Cristolovean (“Celler”) and also in “Mechanically induced Si        layer transfer in hydrogen-implanted Si wafers,” Appl. Phys.        Lett., vol. 76, pp. 2370-2372, 2000 by K. Henttinen, I. Suni,        and S. S. Lau (“Hentinnen”).    -   Porous silicon approaches such as ELTRAN: These are described in        “Eltran, Novel SOI Wafer Technology,” JSAP International, Number        4, July 2001 by T. Yonehara and K. Sakaguchi (“Yonehara”).    -   Bonding a substrate with single crystal layers followed by        Polishing, Time-controlled etch-back or Etch-stop layer        controlled etch-back to thin the bonded substrate: These are        described in U.S. Pat. No. 6,806,171 by A. Ulyashin and A.        Usenko (“Ulyashin”) and “Enabling SOI-Based Assembly Technology        for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDM        Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L.        Shi, S. M. Alam, D. J. Frank, S. E. Steen, J. Vichiconti, D.        Posillico, M. Cobb, S. Medd, J. Patel, S. Goma, D.        DiMilia, M. T. Robson, E. Duch, M. Farinelli, C. Wang, R. A.        Conti, D. M. Canaperi, L. Deligianni, A. Kumar, K. T.        Kwietniak, C. D'Emic, J. Ott, A. M. Young, K. W. Guarini, and M.        Ieong (“Topol”).    -   Bonding a wafer with a Gallium Nitride film epitaxially grown on        a sapphire substrate followed by laser lift-off for removing the        transparent sapphire substrate: This method may be suitable for        deposition of Gallium Nitride thin films, and is described in        U.S. Pat. No. 6,071,795 by Nathan W. Cheung, Timothy D. Sands        and William S. Wong (“Cheung”).    -   Rubber stamp layer transfer: This is described in “Solar cells        sliced and diced,” 19 May 2010, Nature News.

This process of constructing RGB LEDs could include several steps thatoccur in a sequence from Step (A) to Step (S). Many of them share commoncharacteristics, features, modes of operation, etc. When the samereference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams—particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 4A. A red LED wafer 436 is constructedon a GaAs substrate 402 and includes a N-type confinement layer 404, amultiple quantum well (MQW) 406, a P-type confinement layer 408, anoptional reflector 409 and an ITO current spreader 410. Examples ofmaterials used to construct these layers, include, but are not limitedto, doped AlInGaP for the N-type confinement layer 404 and P-typeconfinement layer 408, the multiple quantum well layer 406 could be ofAlInGaP and GaInP and the optional reflector 409 could be a distributedBragg Reflector. A double heterostructure configuration or singlequantum well configuration could be used instead of a multiple quantumwell configuration. Various other material types and configurationscould be used for constructing the red LEDs for this process. Yetanother wafer is constructed with a green LED. The green LED wafer 438is constructed on a sapphire or SiC or bulk-GaN substrate 412 andincludes a N-type confinement layer 414, a multiple quantum well (MQW)416, a buffer layer 418, a P-type confinement layer 420, an optionalreflector 421 and an ITO current spreader 422. Yet another wafer isconstructed with a blue LED. The blue LED wafer 440 is constructed on asapphire or SiC or bulk-GaN substrate 424 and includes a N-typeconfinement layer 426, a multiple quantum well (MQW) 428, a buffer layer430, a P-type confinement layer 432, an optional reflector 433 and anITO current spreader 434. Examples of materials used to construct theseblue and green LED layers, include, but are not limited to, doped GaNfor the N-type and P-type confinement layers 414, 420, 426 and 432,AlGaN for the buffer layers 430 and 418 and InGaN/GaN for the multiplequantum wells 416 and 428. The optional reflectors 421 and 433 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.

Step (B) is illustrated in FIG. 4B. The blue LED wafer 440 from FIG. 4Ais used for this step. Various elements in FIG. 4B such as, for example,424, 426, 428, 430, 432, 433, and 434 have been previously described.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 442. Alternatively, helium could be used for this step.

Step (C) is illustrated in FIG. 4C. A glass substrate 446 is taken andan ITO layer 444 is deposited atop it.

Step (D) is illustrated in FIG. 4D. The wafer shown in FIG. 4B isflipped and bonded atop the wafer shown in FIG. 4C using ITO-ITObonding. Various elements in FIG. 4D such as 424, 426, 428, 430, 432,433, 434, 442, 446, and 444 have been previously described. The ITOlayer 444 is essentially bonded to the ITO layer 434 using anoxide-to-oxide bonding process.

Step (E) is illustrated in FIG. 4E. Various elements in FIG. 4E such as424, 426, 428, 430, 432, 433, 434, 442, 446, and 444 have beenpreviously described. An ion-cut process is conducted to cleave thestructure shown in FIG. 4D at the hydrogen implant plane 442. Thision-cut process may use a mechanical cleave. An anneal process could beutilized for the cleave as well. After the cleave, a chemical mechanicalpolish (CMP) process is conducted to planarize the surface. The N-typeconfinement layer present after this cleave and CMP process is indicatedas 427.

Step (F) is illustrated in FIG. 4F. Various elements in FIG. 4F such as446, 444, 434, 433, 432, 430, 428, and 427 have been previouslydescribed. An ITO layer 448 is deposited atop the N-type confinementlayer 427.

Step (G) is illustrated in FIG. 4G. The green LED wafer 438 shown inStep (A) is used for this step. Various elements in FIG. 4G such as 412,414, 416, 418, 420, 421, and 422 have been described previously.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 450. Alternatively, helium could be used for this step.

Step (H) is illustrated in FIG. 4H. The structure shown in FIG. 4G isflipped and bonded atop the structure shown in FIG. 4F using ITO-ITObonding. Various elements in FIG. 4H such as 446, 444, 434, 433, 432,430, 428, 427, 448, 412, 414, 416, 418, 420, 421, 422, and 450 have beendescribed previously.

Step (I) is illustrated in FIG. 4I. The structure shown in FIG. 4H iscleaved at the hydrogen plane indicated by 450. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 4I such as 446, 444, 434, 433, 432, 430, 428,427, 448, 416, 418, 420, 421, and 422 have been described previously.The N-type confinement layer present after this cleave and CMP processis indicated as 415.

Step (J) is illustrated in FIG. 4J. An ITO layer 452 is deposited atopthe structure shown in FIG. 4I. Various elements in FIG. 4J such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, and 422have been described previously.

Step (K) is illustrated in FIG. 4K. The red LED wafer 436 shown in Step(A) is used for this step. Various elements in FIG. 4K such as 402, 404,406, 408, 409, and 410 have been described previously. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines454. Alternatively, helium could be used for this step.

Step (L) is illustrated in FIG. 4L. The structure shown in FIG. 4K isflipped and bonded atop the structure shown in FIG. 4J using ITO-ITObonding. Various elements in FIG. 4L such as 446, 444, 434, 433, 432,430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 402, 404, 406,408, 409, 410, and 454 have been described previously.

Step (M) is illustrated in FIG. 4M. The structure shown in FIG. 4L iscleaved at the hydrogen plane 454. A mechanical force could be used forthis cleave. Alternatively, an anneal could be used. A CMP process isthen conducted to planarize the surface. The N-type confinement layerpresent after this process is indicated as 405. Various elements in FIG.4M such as 446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420,421, 415, 422, 452, 406, 408, 409, and 410 have been describedpreviously.

Step (N) is illustrated in FIG. 4N. An ITO layer 456 is deposited atopthe structure shown in FIG. 4M. Various elements in FIG. 4M such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422,452, 406, 408, 409, 410, and 405 have been described previously.

Step (O) is illustrated in FIG. 4O. A reflecting material layer 458,constructed for example with Aluminum or Silver, is deposited atop thestructure shown in FIG. 4N. Various elements in FIG. 4O such as 446,444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422,452, 406, 408, 409, 410, 456, and 405 have been described previously.

Step (P) is illustrated in FIG. 4P. The process of making contacts tovarious layers and packaging begins with this step. A contact andbonding process similar to the one used in “High-power AlGaInN flip-chiplight-emitting diodes,” Applied Physics Letters, vol. 78, no. 22, pp.3379-3381, May 2001, by Wierer, J. J.; Steigerwald, D. A.; Krames, M.R.; OShea, J. J.; Ludowise, M. J.; Christenson, G.; Shen, Y.-C.; Lowery,C.; Martin, P. S.; Subramanya, S.; Gotz, W.; Gardner, N. F.; Kern, R.S.; Stockman, S. A. is used. Vias 460 are etched to different layers ofthe LED stack. Various elements in FIG. 4P such as 446, 444, 434, 433,432, 430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 406, 408,409, 410, 456, 405, and 458 have been described previously. After thevia holes 460 are etched, they may optionally be filled with an oxidelayer and polished with CMP. This fill with oxide may be optional, andthe preferred process may be to leave the via holes as such withoutfill. Note that the term contact holes could be used instead of the termvia holes. Similarly, the term contacts could be used instead of theterm vias.

Step (Q) is illustrated in FIG. 4Q. Aluminum is deposited to fill viaholes 460 from FIG. 4P. Following this deposition, a lithography andetch process is utilized to define the aluminum metal to form vias 462.The vias 462 are smaller in diameter than the via holes 460 shown inFIG. 4P. Various elements in FIG. 4Q such as 446, 444, 434, 433, 432,430, 428, 427, 448, 416, 418, 420, 421, 415, 422, 452, 406, 408, 409,410, 456, 405, 460, and 458 have been described previously.

Step (R) is illustrated in FIG. 4R. A nickel layer 464 and a solderlayer 466 are formed using standard procedures. Various elements in FIG.4R such as 446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420,421, 415, 422, 452, 406, 408, 409, 410, 456, 405, 460, 462, and 458 havebeen described previously.

Step (S) is illustrated in FIG. 4S. The solder layer 466 is then bondedto pads on a silicon sub-mount 468. Various elements in FIG. 4S such as446, 444, 434, 433, 432, 430, 428, 427, 448, 416, 418, 420, 421, 415,422, 452, 406, 408, 409, 410, 456, 405, 460, 462, 458, 464, and 466 havebeen described previously. The configuration of optional reflectors 433,421, and 409 determines light output coming from the LED. A preferredembodiment of this invention may not have a reflector 433, and may havethe reflector 421 (reflecting only the blue light produced by multiplequantum well 428) and the reflector 409 (reflecting only the green lightproduced by multiple quantum well 416). In the process described in FIG.4A-FIG. 4S, the original substrates in FIG. 4A, namely 402, 412 and 424,can be reused after ion-cut. This reuse may make the process morecost-effective.

FIGS. 5A-Q describe an embodiment of this invention, where RGB LEDs arestacked with ion-cut technology, wire bond packaging and conductiveoxide bonding. Essentially, smart-layer transfer is utilized toconstruct this embodiment of the invention. This process of constructingRGB LEDs could include several steps that occur in a sequence from Step(A) to Step (Q). Many of the steps share common characteristics,features, modes of operation, etc. When the same reference numbers areused in different drawing figures, they are used to indicate analogous,similar or identical structures to enhance the understanding of thepresent invention by clarifying the relationships between the structuresand embodiments presented in the various diagrams-particularly inrelating analogous, similar or identical functionality to differentphysical structures.

Step (A): This is illustrated using FIG. 5A. A red LED wafer 536 isconstructed on a GaAs substrate 502 and includes a N-type confinementlayer 504, a multiple quantum well (MQW) 506, a P-type confinement layer508, an optional reflector 509 and an ITO current spreader 510. Examplesof materials used to construct these layers, include, but are notlimited to, doped AlInGaP for the N-type confinement layer 504 andP-type confinement layer 508, the multiple quantum well layer 506 couldbe of AlInGaP and GaInP and the optional reflector 509 could be adistributed Bragg Reflector. A double heterostructure configuration orsingle quantum well configuration could be used instead of a multiplequantum well configuration. Various other material types andconfigurations could be used for constructing the red LEDs for thisprocess. Yet another wafer is constructed with a green LED. The greenLED wafer 538 is constructed on a sapphire or SiC or bulk-GaN substrate512 and includes a N-type confinement layer 514, a multiple quantum well(MQW) 516, a buffer layer 518, a P-type confinement layer 520, anoptional reflector 521 and an ITO current spreader 522. Yet anotherwafer is constructed with a blue LED. The blue LED wafer 540 isconstructed on a sapphire or SiC or bulk-GaN substrate 524 and includesa N-type confinement layer 526, a multiple quantum well (MQW) 528, abuffer layer 530, a P-type confinement layer 532, an optional reflector533 and an ITO current spreader 534. Examples of materials used toconstruct these blue and green LED layers, include, but are not limitedto, doped GaN (for the N-type and P-type confinement layers 514, 520,526, and 532), AlGaN (for the buffer layers 530 and 518), and InGaN/GaN(for the multiple quantum wells 516 and 528). The optional reflectors521 and 533 could be distributed Bragg Reflectors or some other type ofreflectors. Various other material types and configurations could beused for constructing blue and green LEDs for this process.

Step (B) is illustrated in FIG. 5B. The red LED wafer 536 from FIG. 5Ais used for this step. Various elements in FIG. 5B such as 502, 504,506, 508, 509, and 510 have been previously described. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines542. Alternatively, helium could be used for this step.

Step (C) is illustrated in FIG. 5C. A silicon substrate 546 is taken andan ITO layer 544 is deposited atop it.

Step (D) is illustrated in FIG. 5D. The wafer shown in FIG. 5B isflipped and bonded atop the wafer shown in FIG. 5C using ITO-ITObonding. Various elements in FIG. 5D such as 502, 504, 506, 508, 509,510, 542, 544, and 546 have been previously described. The ITO layer 544is essentially bonded to the ITO layer 510 using an oxide-to-oxidebonding process.

Step (E) is illustrated in FIG. 5E. Various elements in FIG. 5E such as506, 508, 509, 510, 544 and 546 have been previously described. Anion-cut process is conducted to cleave the structure shown in FIG. 5D atthe hydrogen implant plane 542. This ion-cut process could preferablyuse a mechanical cleave. An anneal process could be utilized for thecleave as well. After the cleave, a chemical mechanical polish (CMP)process is conducted to planarize the surface. The N-type confinementlayer present after this cleave and CMP process is indicated as 505.

Step (F) is illustrated in FIG. 5F. Various elements in FIG. 5F such as505, 506, 508, 509, 510, 544, and 546 have been previously described. AnITO layer 548 is deposited atop the N-type confinement layer 505.

Step (G) is illustrated in FIG. 5G. The green LED wafer 538 shown inStep (A) is used for this step. Various elements in FIG. 5G such as 512,514, 516, 518, 520, 521, and 522 have been described previously.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 550. Alternatively, helium could be used for this step.

Step (H) is illustrated in FIG. 5H. The structure shown in FIG. 5G isflipped and bonded atop the structure shown in FIG. 5F using ITO-ITObonding. Various elements in FIG. 5H such as 505, 506, 508, 509, 510,544, 546, 548, 512, 514, 516, 518, 520, 521, 550, and 522 have beendescribed previously.

Step (I) is illustrated in FIG. 5I. The structure shown in FIG. 5H iscleaved at the hydrogen plane indicated by 550. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 5I such as 505, 506, 508, 509, 510, 544, 546,548, 516, 518, 520, 521, and 522 have been described previously. TheN-type confinement layer present after this cleave and CMP process isindicated as 515.

Step (J) is illustrated using FIG. 5J. An ITO layer 552 is depositedatop the structure shown in FIG. 5I. Various elements in FIG. 5J such as505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521, 515, and 522have been described previously.

Step (K) is illustrated using FIG. 5K. The blue LED wafer 540 from FIG.5A is used for this step. Various elements in FIG. 5K such as 524, 526,528, 530, 532, 533, and 534 have been previously described. Hydrogen isimplanted into the wafer at a certain depth indicated by dotted lines554. Alternatively, helium could be used for this step.

Step (L) is illustrated in FIG. 5L. The structure shown in FIG. 5K isflipped and bonded atop the structure shown in FIG. 5J using ITO-ITObonding. Various elements in FIG. 4L such as 505, 506, 508, 509, 510,544, 546, 548, 516, 518, 520, 521, 515, 522, 552, 524, 526, 528, 530,532, 533, 554, and 534 have been described previously.

Step (M) is illustrated in FIG. 5M. The structure shown in FIG. 5L iscleaved at the hydrogen plane 554. A mechanical force could be used forthis cleave. Alternatively, an anneal could be used. A CMP process isthen conducted to planarize the surface. The N-type confinement layerpresent after this process is indicated as 527. Various elements in FIG.5M such as 505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521,515, 522, 552, 528, 530, 532, 533, and 534 have been describedpreviously.

Step (N) is illustrated in FIG. 5N. An ITO layer 556 is deposited atopthe structure shown in FIG. 5M. Various elements in FIG. 5N such as 505,506, 508, 509, 510, 544, 546, 548, 516, 518, 520, 521, 515, 522, 552,528, 530, 532, 533, and 534 have been described previously.

Step (O) is illustrated in FIG. 5O. The process of making contacts tovarious layers and packaging begins with this step. Various elements inFIG. 5O such as 505, 506, 508, 509, 510, 544, 546, 548, 516, 518, 520,521, 515, 522, 552, 528, 530, 532, 533, 556, and 534 have been describedpreviously. Via holes 560 are etched to different layers of the LEDstack. After the via holes 560 are etched, they may optionally be filledwith an oxide layer and polished with CMP. This fill with oxide may beoptional, and the preferred process may be to leave the via holes assuch without fill.

Step (P) is illustrated in FIG. 5P. Aluminum is deposited to fill viaholes 560 from FIG. 5O. Following this deposition, a lithography andetch process is utilized to define the aluminum metal to form via holes562. Various elements in FIG. 5P such as 505, 506, 508, 509, 510, 544,546, 548, 516, 518, 520, 521, 515, 522, 552, 528, 530, 532, 533, 556,560, and 534 have been described previously.

Step (Q) is illustrated in FIG. 5Q. Bond pads 564 are constructed andwire bonds are attached to these bond pads following this step. Variouselements in FIG. 5Q such as 505, 506, 508, 509, 510, 544, 546, 548, 516,518, 520, 521, 515, 522, 552, 528, 530, 532, 533, 556, 560, 562, and 534have been described previously. The configuration of optional reflectors533, 521 and 509 determines light output coming from the LED. Thepreferred embodiment of this invention is to have reflector 533 reflectonly blue light produced by multiple quantum well 528, to have thereflector 521 reflecting only green light produced by multiple quantumwell 516 and to have the reflector 509 reflect light produced bymultiple quantum well 506. In the process described in FIG. 5A-FIG. 5Q,the original substrates in FIG. 5A, namely 502, 512 and 524, can bere-used after ion-cut. This may make the process more cost-effective.

FIGS. 6A-6L show an alternative embodiment of this invention, wherestacked RGB LEDs are formed with ion-cut technology, flip-chip packagingand aligned bonding. A smart layer transfer process, ion-cut, istherefore utilized. This process of constructing RGB LEDs could includeseveral steps that occur in a sequence from Step (A) to Step (K). Manyof the steps share common characteristics, features, modes of operation,etc. When identical reference numbers are used in different drawingfigures, they are used to indicate analogous, similar or identicalstructures to enhance the understanding of the present invention byclarifying the relationships between the structures and embodimentspresented in the various diagrams-particularly in relating analogous,similar or identical functionality to different physical structures.

Step (A) is illustrated in FIG. 6A. A red LED wafer 636 is constructedon a GaAs substrate 602 and includes a N-type confinement layer 604, amultiple quantum well (MQW) 606, a P-type confinement layer 608, anoptional reflector 609 and an ITO current spreader 610. Above the ITOcurrent spreader 610, a layer of silicon oxide 692 is deposited,patterned, etched and filled with a metal 690 (e.g., tungsten) which isthen CMPed. Examples of materials used to construct these layers,include, but are not limited to, doped AlInGaP for the N-typeconfinement layer 604 and P-type confinement layer 608, the multiplequantum well layer 606 could be of AlInGaP and GaInP and the optionalreflector 609 could be a distributed Bragg Reflector. A doubleheterostructure configuration or single quantum well configuration couldbe used instead of a multiple quantum well configuration. Various othermaterial types and configurations could be used for constructing the redLEDs for this process. Yet another wafer is constructed with a greenLED. The green LED wafer 638 is constructed on a sapphire or SiC orbulk-GaN substrate 612 and includes a N-type confinement layer 614, amultiple quantum well (MQW) 616, a buffer layer 618, a P-typeconfinement layer 620, an optional reflector 621 and an ITO currentspreader 622. Above the ITO current spreader 622, a layer of siliconoxide 696 is deposited, patterned, etched and filled with a metal 694(e.g., tungsten) which is then CMPed. Yet another wafer is constructedwith a blue LED. The blue LED wafer 640 is constructed on a sapphire orSiC or bulk-GaN substrate 624 and includes a N-type confinement layer626, a multiple quantum well (MQW) 628, a buffer layer 630, a P-typeconfinement layer 632, an optional reflector 633 and an ITO currentspreader 634. Above the ITO current spreader 634, a layer of silicondioxide 698 is deposited. Examples of materials used to construct theseblue and green LED layers, include, but are not limited to, doped GaNfor the N-type and P-type confinement layers 614, 620, 626 and 632,AlGaN for the buffer layers 630 and 618 and InGaN/GaN for the multiplequantum wells 616 and 628. The optional reflectors 621 and 633 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.

Step (B) is illustrated in FIG. 6B. The blue LED wafer 640 from FIG. 6Ais used for this step. Various elements in FIG. 6B such as 624, 626,628, 630, 632, 633, 698, and 634 have been previously described.Hydrogen is implanted into the wafer at a certain depth indicated bydotted lines 642. Alternately, helium could be used for this step.

Step (C) is illustrated in FIG. 6C. A glass substrate 646 is taken and asilicon dioxide layer 688 is deposited atop it.

Step (D) is illustrated in FIG. 6D. The wafer shown in FIG. 6B isflipped and bonded atop the wafer shown in FIG. 6C using oxide-oxidebonding. Various elements in FIG. 6D such as 624, 626, 628, 630, 632,633, 698, 642, 646, 688, and 634 have been previously described. Theoxide layer 688 is essentially bonded to the oxide layer 698 using anoxide-to-oxide bonding process.

Step (E) is illustrated in FIG. 6E. Various elements in FIG. 6E such as628, 630, 632, 633, 698, 646, 688, and 634 have been previouslydescribed. An ion-cut process is conducted to cleave the structure shownin FIG. 6D at the hydrogen implant plane 642. This ion-cut process maybe preferably using a mechanical cleave. An anneal process could beutilized for the cleave as well. After the cleave, a chemical mechanicalpolish (CMP) process is conducted to planarize the surface. The N-typeconfinement layer present after this cleave and CMP process is indicatedas 627.

Step (F) is illustrated in FIG. 6F. Various elements in FIG. 6F such as628, 630, 632, 633, 698, 646, 688, 627, and 634 have been previouslydescribed. An ITO layer 648 is deposited atop the N-type confinementlayer 627. Above the ITO layer 648, a layer of silicon oxide 686 isdeposited, patterned, etched and filled with a metal 684 (e.g.,tungsten) which is then CMPed.

Step (G) is illustrated in FIG. 6G. The green LED wafer 638 shown inStep (A) is used for this step. Various elements in FIG. 6G such as 612,614, 616, 618, 620, 621, 696, 694, and 622 have been describedpreviously. Hydrogen is implanted into the wafer at a certain depthindicated by dotted lines 650. Alternatively, helium could be used forthis step.

Step (H) is illustrated in FIG. 6H. The structure shown in FIG. 6G isflipped and bonded atop the structure shown in FIG. 6F using oxide-oxidebonding. The metal regions 694 and 684 on the bonded wafers are alignedto each other. Various elements in FIG. 6H such as 628, 630, 632, 633,698, 646, 688, 627, 634, 648, 686, 684, 612, 614, 616, 618, 620, 621,696, 694, 650, and 622 have been described previously.

Step (I) is illustrated in FIG. 6I. The structure shown in FIG. 6H iscleaved at the hydrogen plane indicated by 650. This cleave process maybe preferably done with a mechanical force. Alternatively, an annealcould be used. A CMP process is conducted to planarize the surface.Various elements in FIG. 6I such as 628, 630, 632, 633, 698, 646, 688,627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, and 622 have beendescribed previously. The N-type confinement layer present after thiscleave and CMP process is indicated as 615.

Step (J) is illustrated in FIG. 6J. An ITO layer 652 is deposited atopthe structure shown in FIG. 6I. Above the ITO layer 652, a layer ofsilicon oxide 682 is deposited, patterned, etched and filled with ametal 680 (e.g., tungsten) which is then CMPed.

Various elements in FIG. 6J such as 628, 630, 632, 633, 698, 646, 688,627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, 615, and 622 havebeen described previously.

Step (K) is illustrated in FIG. 6K. Using procedures similar to Step(G)-Step (J), the red LED layer is transferred atop the structure shownin FIG. 6J. The N-type confinement layer after ion-cut is indicated by605. An ITO layer 656 is deposited atop the N-type confinement layer605. Various elements in FIG. 6K such as 628, 630, 632, 633, 698, 646,688, 627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, 615, 690,692, 610, 609, 608, 606, and 622 have been described previously.

Step (L) is illustrated in FIG. 6L. Using flip-chip packaging proceduressimilar to those described in FIG. 4A-FIG. 4S, the RGB LED stack shownin FIG. 6K is attached to a silicon sub-mount 668. 658 indicates areflecting material, 664 is a nickel layer, 666 represents solder bumps,670 is an aluminum via, and 672 is either an oxide layer or an air gap.Various elements in FIG. 6K such as 628, 630, 632, 633, 698, 646, 688,627, 634, 648, 686, 684, 616, 618, 620, 621, 696, 694, 615, 690, 692,610, 609, 608, 606, 605, 656, and 622 have been described previously.The configuration of optional reflectors 633, 621 and 609 determineslight output coming from the LED.

A preferred embodiment of this invention may not have a reflector 633,but may have the reflector 621 (reflecting only the blue light producedby multiple quantum well 628) and the reflector 609 (reflecting only thegreen light produced by multiple quantum well 616). In the processdescribed in FIG. 6A-FIG. 6L, the original substrates in FIG. 6A, namely602, 612, and 624, can be re-used after ion-cut. This may make theprocess more cost-effective.

FIGS. 7A-L illustrate an embodiment of this invention, where stacked RGBLEDs are formed with laser lift-off, substrate etch, flip-chip packagingand conductive oxide bonding. Essentially, smart layer transfertechniques are used. This process could include several steps that occurin a sequence from Step (A) to Step (M). Many of the steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams-particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A): This is illustrated using FIG. 7A. A red LED wafer 736 isconstructed on a GaAs substrate 702 and includes a N-type confinementlayer 704, a multiple quantum well (MQW) 706, a P-type confinement layer708, an optional reflector 709 and an ITO current spreader 710. Examplesof materials used to construct these layers, include, but are notlimited to, doped AlInGaP for the N-type confinement layer 704 andP-type confinement layer 708, the multiple quantum well layer 706 couldbe of AlInGaP and GaInP and the optional reflector 409 could be adistributed Bragg Reflector. A double heterostructure configuration orsingle quantum well configuration could be used instead of a multiplequantum well configuration. Various other material types andconfigurations could be used for constructing the red LEDs for thisprocess. Yet another wafer is constructed with a green LED. The greenLED wafer 738 is constructed on a sapphire substrate 712 (or some othertransparent substrate) and includes a N-type confinement layer 714, amultiple quantum well (MQW) 716, a buffer layer 718, a P-typeconfinement layer 720, an optional reflector 721 and an ITO currentspreader 722. Yet another wafer is constructed with a blue LED. The blueLED wafer 740 is constructed on a sapphire substrate 724 (or some othertransparent substrate) and includes a N-type confinement layer 726, amultiple quantum well (MQW) 728, a buffer layer 730, a P-typeconfinement layer 732, an optional reflector 733 and an ITO currentspreader 734. Examples of materials used to construct these blue andgreen LED layers, include, but are not limited to, doped GaN for theN-type and P-type confinement layers 714, 720, 726 and 732, AlGaN forthe buffer layers 730 and 718 and InGaN/GaN for the multiple quantumwells 716 and 728. The optional reflectors 721 and 733 could bedistributed Bragg Reflectors or some other type of reflectors. Variousother material types and configurations could be used for constructingblue and green LEDs for this process.

Step (B) is illustrated in FIG. 7B. A glass substrate 746 is taken andan ITO layer 744 is deposited atop it.

Step (C) is illustrated in FIG. 7C. The blue LED wafer 740 shown in FIG.7A is flipped and bonded atop the wafer shown in FIG. 7B using ITO-ITObonding. Various elements in FIG. 7C such as 724, 726, 728, 730, 732,733, 734, 746, and 744 have been previously described. The ITO layer 744is essentially bonded to the ITO layer 734 using an oxide-to-oxidebonding process.

Step (D) is illustrated in FIG. 7D. A laser is used to shine radiationthrough the sapphire substrate 724 of FIG. 7C and a laser lift-offprocess is conducted. The sapphire substrate 724 of FIG. 7C is removedwith the laser lift-off process. Further details of the laser lift-offprocess are described in U.S. Pat. No. 6,071,795 by Nathan W. Cheung,Timothy D. Sands and William S. Wong (“Cheung”). A CMP process isconducted to planarize the surface of the N confinement layer 727 afterlaser lift-off of the sapphire substrate. Various elements in FIG. 7Dsuch as 728, 730, 732, 733, 734, 746, and 744 have been previouslydescribed.

Step (E) is illustrated in FIG. 7E. Various elements in FIG. 7E such as728, 730, 732, 733, 734, 746, 727, and 744 have been previouslydescribed. An ITO layer 748 is deposited atop the N confinement layer727.

Step (F) is illustrated in FIG. 7F. The green LED wafer 738 is flippedand bonded atop the structure shown in FIG. 7E using ITO-ITO bonding oflayers 722 and 748. Various elements in FIG. 7F such as 728, 730, 732,733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 714, 712 and 744 havebeen previously described.

Step (G) is illustrated in FIG. 7G. A laser is used to shine radiationthrough the sapphire substrate 712 of FIG. 7F and a laser lift-offprocess is conducted. The sapphire substrate 712 of FIG. 7F is removedwith the laser lift-off process. A CMP process is conducted to planarizethe surface of the N-type confinement layer 715 after laser lift-off ofthe sapphire substrate. Various elements in FIG. 7G such as 728, 730,732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, and 744 have beenpreviously described.

Step (H) is illustrated in FIG. 7H. An ITO layer 752 is deposited atopthe N-type confinement layer 715. Various elements in FIG. 7H such as728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715,and 744 have been previously described.

Step (I) is illustrated in FIG. 7I. The red LED wafer 736 from FIG. 7Ais flipped and bonded atop the structure shown in FIG. 7H using ITO-ITObonding of layers 710 and 752. Various elements in FIG. 7I such as 728,730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715, 752,710, 709, 708, 706, 704, 702, and 744 have been previously described.

Step (J) is illustrated in FIG. 7J. The GaAs substrate 702 from FIG. 7Iis removed using etch and/or CMP. Following this etch and/or CMPprocess, the N-type confinement layer 704 of FIG. 7I is planarized usingCMP to form the N-type confinement layer 705. Various elements in FIG.7J such as 728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718,716, 715, 752, 710, 709, 708, 706, and 744 have been previouslydescribed.

Step (K) is illustrated in FIG. 7K. An ITO layer 756 is deposited atopthe N confinement layer 705 of FIG. 7J. Various elements in FIG. 7K suchas 728, 730, 732, 733, 734, 746, 727, 748, 722, 721, 720, 718, 716, 715,752, 710, 709, 708, 706, 705, and 744 have been previously described.

Step (L) is illustrated in FIG. 7L. Using flip-chip packaging proceduressimilar to those described in FIG. 4A-FIG. 4S, the RGB LED stack shownin FIG. 7K is attached to a silicon sub-mount 768. 758 indicates areflecting material, 764 is a nickel layer, 766 represents solder bumps,762 is an aluminum via, and 772 is either an oxide layer or an air gap.Various elements in FIG. 7L such as 728, 730, 732, 733, 734, 746, 727,748, 722, 721, 720, 718, 716, 715, 752, 710, 709, 708, 706, 705, and 756have been described previously. The configuration of optional reflectors733, 721 and 709 determines light output coming from the LED. Thepreferred embodiment of this invention may not have a reflector 733, butmay have the reflector 721 (reflecting only the blue light produced bymultiple quantum well 728) and the reflector 709 (reflecting only thegreen light produced by multiple quantum well 716).

FIGS. 8A-B show an embodiment of this invention, where stacked RGB LEDsare formed from a wafer having red LED layers and another wafer havingboth green and blue LED layers. Therefore, a smart layer transferprocess is used to form the stacked RGB LED. FIG. 8A shows that a redLED wafer 836 and another wafer called a blue-green LED wafer 836 areused. The red LED wafer 836 is constructed on a GaAs substrate 802 andincludes a N-type confinement layer 804, a multiple quantum well (MQW)806, a P-type confinement layer 808, an optional reflector 809 and anITO current spreader 810. Examples of materials used to construct theselayers, include, but are not limited to, doped AlInGaP for the N-typeconfinement layer 804 and P-type confinement layer 808, the multiplequantum well layer 806 could be of AlInGaP and GaInP and the optionalreflector 809 could be a distributed Bragg Reflector. A doubleheterostructure configuration or single quantum well configuration couldbe used instead of a multiple quantum well configuration. Various othermaterial types and configurations could be used for constructing the redLEDs for this process. The blue-green LED wafer 838 is constructed on asapphire or bulk GaN or SiC substrate 812 (or some other transparentsubstrate) and includes a N-type confinement layer 814, a green multiplequantum well (MQW) 816, a blue multiple quantum well 817, a buffer layer818, a P-type confinement layer 820, an optional reflector 821, and anITO current spreader 822. Examples of materials used to construct theblue-green LED wafers, include, but are not limited to, doped GaN forthe N-type and P-type confinement layers 814, 820, AlGaN for the bufferlayer 818 and InGaN/GaN for the multiple quantum wells 816 and 817. Theoptional reflector 821 could be a distributed Bragg Reflector or someother type of reflector. The optional reflector 821 could alternativelybe built between the N-type confinement layer 814 or below it, and thisis valid for all LEDs discussed in the patent application. Various othermaterial types and configurations could be used for constructingblue-green LED wafers for this process. Using smart layer transferprocedures similar to those shown in FIG. 4-FIG. 7, the stacked RGB LEDstructure shown in FIG. 8B is constructed. Various elements in FIG. 8Bsuch as 806, 808, 809, 810, 816, 817, 818, 820, 821, and 822 have beendescribed previously. 846 is a glass substrate, 844 is an ITO layer, 815is a N-type confinement layer for a blue-green LED, 852 is an ITO layer,805 is a N-type confinement layer for a red LED, 856 is an ITO layer,858 is a reflecting material such as, for example, silver or aluminum,864 is a nickel layer, 866 is a solder layer, 862 is a contact layerconstructed of aluminum or some other metal, 860 may be preferably anair gap but could be an oxide layer and 868 is a silicon sub-mount. Theconfiguration of optional reflectors 821 and 809 determines lightproduced by the LED. For the configuration shown in FIG. 8B, thepreferred embodiment may not have the optional reflector 821 and mayhave the optional reflector 809 reflecting light produced by the blueand green quantum wells 816 and 817.

FIG. 9 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits for the LED built onthe silicon sub-mount. Procedures similar to those described in FIG.4-FIG. 7 are utilized for constructing and packaging the LED. Controland driver circuits are integrated on the silicon sub-mount 968 and canbe used for controlling and driving the stacked RGB LED. 946 is a glasssubstrate, 944 and 934 are ITO layers, 933 is an optional reflector, 932is a P-type confinement layer for a blue LED, 930 is a buffer layer fora blue LED, 928 is a blue multiple quantum well, 927 is a N-typeconfinement layer for a blue LED, 948 and 922 are ITO layers, 921 is anoptional reflector, 920 is a P-type confinement layer for a green LED,918 is a buffer layer for a green LED, 916 is a multiple quantum wellfor a green LED, 915 is a N-type confinement layer for a green LED, 952and 910 are ITO layers, 909 is a reflector, 908 is a P-type confinementlayer for a red LED, 906 is a red multiple quantum well, 905 is a N-typeconfinement layer for a red LED, 956 is an ITO layer, 958 is areflecting layer such as aluminum or silver, 962 is a metal viaconstructed, for example, out of aluminum, 960 is an air-gap or an oxidelayer, 964 is a nickel layer, and 966 is a solder bump.

FIG. 10 illustrates an embodiment of this invention, where stacked RGBLEDs are formed with control and driver circuits as well as imagesensors for the LED built on the silicon sub-mount 1068. Image sensorsessentially monitor the light coming out of the LED and tune the voltageand current given by control and driver circuits such that light outputof the LED is the right color and intensity. 1046 is a glass substrate,1044 and 1034 are ITO layers, 1033 is an optional reflector, 1032 is aP-type confinement layer for a blue LED, 1030 is a buffer layer for ablue LED, 1028 is a blue multiple quantum well, 1027 is a N-typeconfinement layer for a blue LED, 1048 and 1022 are ITO layers, 1021 isan optional reflector, 1020 is a P-type confinement layer for a greenLED, 1018 is a buffer layer for a green LED, 1016 is a multiple quantumwell for a green LED, 1015 is a N-type confinement layer for a greenLED, 1052 and 1010 are ITO layers, 1009 is a reflector, 1008 is a P-typeconfinement layer for a red LED, 1006 is a red multiple quantum well,1005 is a N-type confinement layer for a red LED, 1056 is an ITO layer,1058 is a reflecting layer such as aluminum or silver, 1062 is a metalvia constructed for example out of aluminum, 1060 is an air-gap or anoxide layer, 1064 is a nickel layer and 1066 is a solder bump. The viahole 1074 helps transfer light produced by the blue multiple quantumwell 1028 reach an image sensor on the silicon sub-mount 1068. The viahole 1072 helps transfer light produced by the green multiple quantumwell 1016 to an image sensor on the silicon sub-mount 1068. The via hole1070 helps transfer light produced by the red multiple quantum well 1006reach an image sensor on the silicon sub-mount 1068. By sampling thelight produced by each of the quantum wells on the LED, voltage andcurrent drive levels to different terminals of the LED can bedetermined. Color tunability, temperature compensation, better colorstability, and many other features can be obtained with this scheme.Furthermore, circuits to communicate wirelessly with the LED can beconstructed on the silicon sub-mount. Light output of the LED can bemodulated by a signal from the user delivered wirelessly to the light.

While three LED layers, namely, red, green, and blue, are shown asstacked in various embodiments of this invention, it will be clear toone skilled in the art based on the present disclosure that more thanthree LED layers can also be stacked. For example, red, green, blue andyellow LED layers can be stacked.

The embodiments of this invention described in FIG. 4-FIG. 10 share afew common features. They have multiple stacked (or overlying) layers,they are constructed using smart layer transfer techniques and at leastone of the stacked layers has a thickness less than 50 microns. Whencleave is done using ion-cut, substrate layers that are removed usingcleave can be reused after a process flow that often includes a CMP.

FIGS. 11A-F show a prior art illustration of phosphor-coated LEDs(pcLEDs) constructed with ion-cut processes. The process begins in FIG.11A with a bulk-GaN substrate 1102, and an oxide layer 1104 is depositedatop it. The oxide layer 1104 is an oxide compatible with GaN. FIG. 11Bdepicts hydrogen being implanted into the structure shown in FIG. 11A ata certain depth (for ion-cut purposes). 1102 and 1104 have beendescribed previously with respect to FIG. 11A. Dotted lines 1106indicate the plane of hydrogen ions. Alternatively, helium can beimplanted instead of hydrogen or hydrogen and helium can beco-implanted. FIG. 11C shows a silicon wafer 1108 with an oxide layer1110 atop it. The structure shown in FIG. 11B is flipped and bonded atopthe structure shown in FIG. 11C using oxide-to-oxide bonding of layers1104 and 1110. This is depicted in FIG. 11D. 1108, 1110 and 1106 havebeen described previously. FIG. 11E shows the next step in the process.Using an anneal, a cleave is conducted at the plane of hydrogen atoms1106 shown in FIG. 11D, and a CMP is done to form GaN layer 1112. 1104,1110 and 1108 have been described previously. FIG. 11F shows thefollowing step in the process. A blue LED 1114 is grown epitaxiallyabove the GaN layer 1112. 1104, 1108 and 1110 have been describedpreviously. A phosphor layer can be coated atop the blue LED 1114 toform a white phosphor coated LED.

There may be some severe challenges with the prior art process shown inFIGS. 11A-F. The thermal expansion coefficients for GaN layers 1112 inFIG. 11F are very different from that for silicon layers 1108. Thisdifference can cause cracks and defects while growing the blue LED layer1114 at high temperatures (>600° C.), which usually occurs. These cracksand defects, in turn, cause bad efficiency and can in turn cause thephosphor coated LED process in FIG. 11A-F to be difficult tomanufacture. Furthermore, an anneal (typically >400° C.) is typicallyused in FIG. 11E to cleave the bulk GaN layers. This can again causeissues with mismatch of thermal expansion co-efficients and causecracking and defects.

FIGS. 12A-F describe an embodiment of this invention, where phosphorcoated LEDs are formed with an ion-cut process (i.e. a smart layertransfer process). It minimizes the problem with mismatch of thermalexpansion co-efficients that is inherent to the process described inFIGS. 11A-F. This process could include several steps as described inthe following sequence:

Step (A): FIG. 12A illustrates this step. A blue LED wafer isconstructed on a bulk-GaN substrate 1216. For discussions within thisdocument, the bulk-GaN substrate could be semi-polar or non-polar orpolar. The blue LED wafer includes a N-type confinement layer 1214, amultiple quantum well (MQW) 1212, a buffer layer 1210, a P-typeconfinement layer 1208, an optional reflector 1204 and an ITO currentspreader 1206. Examples of materials used to construct these blue LEDlayers, include, but are not limited to, doped GaN for the N-type andP-type confinement layers 1214 and 1208, AlGaN for the buffer layer 1210and InGaN/GaN for the multiple quantum wells 1212. The optionalreflector 1204 could be distributed Bragg Reflector, an Aluminum orsilver layer or some other type of reflectors. A silicon dioxide layer1202 is deposited atop the optional reflector 1204.

Step (B): FIG. 12B illustrates this step. The blue LED wafer describedin FIG. 12A has hydrogen implanted into it at a certain depth. Thedotted lines 1218 depict the hydrogen implant. Alternatively, helium canbe implanted. Various elements in FIG. 12B such as 1216, 1214, 1212,1210, 1208, 1206, 1204, and 1202 have been described previously.

Step (C): FIG. 12C illustrates this step. A wafer 1220, preferably ofsilicon, having the same wafer size as the structure in FIG. 12B istaken and an oxide layer 1222 is grown or deposited atop it.

Step (D): FIG. 12D illustrates this step. The structure shown in FIG.12B is flipped and bonded atop the structure shown in FIG. 12C usingoxide-to-oxide bonding of layers 1202 and 1222. Various elements in FIG.12D such as 1216, 1214, 1212, 1210, 1208, 1206, 1204, 1220, 1222, 1218and 1202 have been described previously.

Step (E): FIG. 12E illustrates this step. The structure shown in FIG.12D is cleaved at its hydrogen plane 1218. A mechanical cleave may bepreferably used for this process. However, an anneal could be used aswell. The mechanical cleave process typically happens at roomtemperatures, and therefore can avoid issues with thermal expansionco-efficients mismatch. After cleave, the wafer is planarized and theN-type confinement layer 1215 is formed. Various elements in FIG. 12Esuch as 1212, 1210, 1208, 1206, 1204, 1220, 1222, and 1202 have beendescribed previously. The bulk GaN substrate 1216 from FIG. 12D that hasbeen cleaved away can be reused. This may be attractive from a costperspective, since bulk GaN substrates are quite costly.

Step (F): This is illustrated in FIG. 12F. An ITO layer 1224 isdeposited atop the structure shown in FIG. 12E. Various elements in FIG.12F such as 1212, 1210, 1208, 1206, 1204, 1220, 1222, 1215, 1224, and1202 have been described previously.

A phosphor coating can be applied over the structure shown in FIG. 12Fto produce a phosphor-coated LED. The advantage of the process shown inFIG. 12A-F over the process shown in FIG. 11A-F may include low processtemperatures, even less than 250° C. Therefore, issues with thermalexpansion co-efficients mismatch are substantially mitigated. While thedescription in FIG. 12A-F is for a LED, many other devices, such as, forexample, laser diodes, high power transistors, high frequenciestransistors, special transmitter circuits and many other devices can beconstructed, according to a similar description, with bulk-GaN.

In the description of FIG. 12A-F, silicon is described as a preferredmaterial for the substrate 1220. Silicon has a co-efficient of thermalexpansion of about 2.6 ppm/° C., while bulk-GaN, which is the substrate1216 on which the LED is epitaxially grown, has a co-efficient ofthermal expansion of 5.6 ppm/° C. In an alternate embodiment of thisinvention, the substrate 1220 used in FIG. 12A-F could be constructed ofa material that has a co-efficient of thermal expansion (CTE) fairlyclose to bulk-GaN. Preferably, the CTE of the substrate 1220 could beany value in between (the CTE of bulk GaN-2 ppm/° C.) and (the CTE ofbulk GaN+2 ppm/° C.). Examples of materials that could be used for thesubstrate 1220 could include, but are not limited to, Germanium, thathas a CTE of 5.8 ppm/° C., and various ceramic materials. Having CTE forthe substrate 1220 close to bulk-GaN prevents defects and cracks beingformed due to issues with mismatch of CTE, even if higher temperatureprocessing (>250° C.) is used.

In an alternative embodiment of this invention, the flow in FIG. 11A-Fcan be used with the substrate 1108 having a CTE fairly close to the CTEof bulk GaN. Preferably, the CTE of the substrate 1108 could be anyvalue in between (the CTE of bulk GaN-2 ppm/° C.) and (the CTE of bulkGaN+2 ppm/° C.). Examples of materials that could be used for thesubstrate 1108 could include, but are not limited to, Germanium, thathas a CTE of 5.8 ppm/° C., and various ceramic materials.

NuDisplay Technology:

In displays and microdisplays (small size displays where opticalmagnification is needed), transistors need to be formed on glass orplastic substrates. These substrates typically cannot withstand highprocess temperatures (e.g., >400° C.). Layer transfer can beadvantageously used for constructing displays and microdisplays as well,since it may enable transistors to be processed on these substrates at<400° C. Various embodiments of transistors constructed on glasssubstrates are described in this patent application. These transistorsconstructed on glass substrates could form part of liquid crystaldisplays (LCDs) or other types of displays. It will be clear to thoseskilled in the art based on the present disclosure that these techniquescan also be applied to plastic substrates.

FIGS. 22A-G describe a process for forming recessed channel singlecrystal (or monocrystalline) transistors on glass substrates at atemperature approximately less than 400° C. for display and microdisplayapplications. This process could include several steps that occur in asequence from Step (A) to Step (G). Many of these steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams-particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 13A. A silicon wafer 2202 is taken and an+ region 2204 is formed by ion implantation. Following this formation,a layer of p− Silicon 2206 is epitaxially grown. An oxide layer 2210 isthen deposited. Following this deposition, an anneal is performed toactivate dopants in various layers. It will be clear to one skilled inthe art based on the present disclosure that various other procedurescan be used to get the structure shown in FIG. 13A. Step (B) isillustrated in FIG. 22B. Hydrogen is implanted into the structure shownin FIG. 13A at a certain depth indicated by 2212. Alternatively, Heliumcan be used for this purpose. Various elements in FIG. 22B, such as2202, 2204, 2006, and 2210 have been described previously. Step (C) isillustrated in FIG. 13C. A glass substrate 2214 is taken and a siliconoxide layer 2216 is deposited atop it at compatible temperatures. Step(D) is illustrated in FIG. 13D. Various elements in FIG. 13D, such as2202, 2204, 2206, 2210, 2214, and 2216 have been described previously.The structure shown in FIG. 13B is flipped and bonded to the structureshown in FIG. 13C using oxide-to-oxide bonding of layers 2210 and 2216.Step (E) is illustrated in FIG. 13E. The structure shown in FIG. 13D iscleaved at the hydrogen plane 2212 of FIG. 13D. A CMP is then done toplanarize the surface and yield the n+Si layer 2218. Various otherelements in FIG. 13E, such as 2214, 2216, 2210 and 2206 have beendescribed previously. Step (F) is illustrated in FIG. 13F. Variouselements in FIG. 13F such as 2214, 2216, 2210, and 2206 have beendescribed previously. An oxide layer 2220 is formed using a shallowtrench isolation (STI) process. This helps isolate transistors. Step (G)is illustrated in FIG. 13G. Various elements in FIG. 13G such as 2210,2216, 2220 and 2214 have been described previously. Using etchtechniques, part of the n+ Silicon layer from FIG. 13F and optionally p−Silicon layer from FIG. 13F are etched. After this a thin gatedielectric is deposited, after which a gate dielectrode is deposited.The gate dielectric and gate electrode are then polished away to formthe gate dielectric layer 2224 and gate electrode layer 2222. The n+Silicon layers 2228 and 2226 form the source and drain regions of thetransistors while the p− Silicon region after this step is indicated by2230. Contacts and other parts of the display/microdisplay are thenfabricated. It can be observed that during the whole process, the glasssubstrate substantially always experiences temperatures less than 400°C., or even lower. This is because the crystalline silicon can betransferred atop the glass substrate at a temperature less than 400° C.,and dopants are pre-activated before layer transfer to glass.

FIG. 14A-H describes a process of forming both nMOS and pMOS transistorswith single-crystal silicon on a glass substrate at temperatures lessthan 400° C., and even lower. Ion-cut technology (which is a smart layertransfer technology) is used. While the process flow described is shownfor both nMOS and pMOS on a glass substrate, it could also be used forjust constructing nMOS devices or for just constructing pMOS devices.This process could include several steps that occur in a sequence fromStep (A) to Step (H). Many of these steps share common characteristics,features, modes of operation, etc. When identical reference numbers areused in different drawing figures, they are used to indicate analogous,similar or identical structures to enhance the understanding of thepresent invention by clarifying the relationships between the structuresand embodiments presented in the various diagrams-particularly inrelating analogous, similar or identical functionality to differentphysical structures.

Step (A) is illustrated in FIG. 14A. A p− Silicon wafer 2302 is takenand a n well 2304 is formed on the p− Silicon wafer 2302. Variousadditional implants to optimize dopant profiles can also be done.Following this formation, an isolation process is conducted to formisolation regions 2306. A dummy gate dielectric 2310 made of silicondioxide and a dummy gate electrode 2308 made of polysilicon areconstructed. Step (B) is illustrated in FIG. 14B. Various elements ofFIG. 14B, such as 2302, 2304, 2306, 2308 and 2310 have been describedpreviously. Implants are done to form source-drain regions 2312 and 2314for both nMOS and pMOS transistors. A rapid thermal anneal (RTA) is thendone to activate dopants. Alternatively, a spike anneal or a laseranneal could be done. Step (C) is illustrated in FIG. 14C. Variouselements of FIG. 14C such as 2302, 2304, 2306, 2308, 2310, 2312 and 2314have been described previously. An oxide layer 2316 is deposited andplanarized with CMP. Step (D) is described in FIG. 14D. Various elementsof FIG. 14D such as 2302, 2304, 2306, 2308, 2310, 2312, 2314, and 2316have been described previously. Hydrogen is implanted into the wafer ata certain depth indicated by 2318. Alternatively, helium can beimplanted. Step (E) is illustrated in FIG. 14E. Various elements of FIG.14E such as 2302, 2304, 2306, 2308, 2310, 2312, 2314, 2316, and 2318have been described previously. Using a temporary bonding adhesive, theoxide layer is bonded to a temporary carrier wafer 2320. An example of atemporary bonding adhesive is a polyimide that can be removed by shininga laser. An example of a temporary carrier wafer is glass. Step (F) isdescribed in FIG. 14F. The structure shown in FIG. 14E is cleaved at thehydrogen plane using a mechanical force. Alternatively, an anneal couldbe used. Following this cleave, a CMP is done to planarize the surface.An oxide layer is then deposited. FIG. 14F shows the structure after allthese steps are done, with the deposited oxide layer indicated as 2328.After the cleave, the p− Silicon region is indicated as 2322, the n−Silicon region is indicated as 2324, and the oxide isolation regions areindicated as 2326. Various other elements in FIG. 14F such as 2308,2320, 2312, 2314, 2310, and 2316 have been described previously. Step(G) is described in FIG. 14G. The structure shown in FIG. 14F is bondedto a glass substrate 2332 with an oxide layer 2330 using oxide-to-oxidebonding. Various elements in FIG. 14G such as 2308, 2326, 2322, 2324,2312, 2314, and 2310 have been described previously. Oxide regions 2328and 2330 are bonded together. The temporary carrier wafer from FIG. 14Fis removed by shining a laser through it. A CMP process is thenconducted to reach the surface of the gate electrode 2308. The oxidelayer remaining is denoted as 2334. Step (H) is described in FIG. 14H.Various elements in FIG. 14H such as 2312, 2314, 2328, 2330, 2332, 2334,2326, 2324, and 2322 have been described previously. The dummy gatedielectric and dummy gate electrode are etched away in this step and areplacement gate dielectric 2336 and a replacement gate electrode 2338are deposited and planarized with CMP. Examples of replacement gatedielectrics could be hafnium oxide or aluminum oxide while examples ofreplacement gate electrodes could be TiN or TaN or some other material.Contact formation, metallization and other steps for building adisplay/microdisplay are then conducted. It can be observed that afterattachment to the glass substrate, no process step requires a processingtemperature above 400° C.

FIGS. 24A-F describe an embodiment of this invention, wheresingle-crystal Silicon junction-less transistors are constructed aboveglass substrates at a temperature approximately less than 400° C. Anion-cut process (which is a smart layer transfer process) is utilizedfor this purpose. This process could include several steps that occur ina sequence from Step (A) to Step (F). Many of these steps share commoncharacteristics, features, modes of operation, etc. When identicalreference numbers are used in different drawing figures, they are usedto indicate analogous, similar or identical structures to enhance theunderstanding of the present invention by clarifying the relationshipsbetween the structures and embodiments presented in the variousdiagrams-particularly in relating analogous, similar or identicalfunctionality to different physical structures.

Step (A) is illustrated in FIG. 15A. A glass substrate 2402 is taken anda layer of silicon oxide 2404 is deposited on the glass substrate 2402.

Step (B) is illustrated in FIG. 15B. A p− Silicon wafer 2406 isimplanted with a n+ Silicon layer 2408 above which an oxide layer 2410is deposited. A RTA or spike anneal or laser anneal is conducted toactivate dopants. Following this, hydrogen is implanted into the waferat a certain depth indicated by 2412. Alternatively, helium can beimplanted. Step (C) is illustrated in FIG. 15C. The structure shown inFIG. 15B is flipped and bonded onto the structure shown in FIG. 15Ausing oxide-to-oxide bonding. This bonded structure is cleaved at itshydrogen plane, after which a CMP is done. FIG. 15C shows the structureafter all these processes are completed. 2414 indicates the n+Si layer,while 2402, 2404, and 2410 have been described previously.

Step (D) is illustrated in FIG. 15D. A lithography and etch process isconducted to pattern the n+ Silicon layer 2414 in FIG. 15C to form n+Silicon regions 2418 in FIG. 15D. The glass substrate is indicated as2402 and the bonded oxide layers 2404 and 2410 are shown as well.

Step (E) is illustrated in FIG. 15E. A gate dielectric 2420 and gateelectrode 2422 are deposited, following which a CMP is done. 2402 is asdescribed previously. The n+Si regions 2418 are not visible in thisfigure, since they are covered by the gate electrode 2422. Oxide regions2404 and 2410 have been described previously.

Step (F) is illustrated in FIG. 15F. The gate dielectric 2420 and gateelectrode 2422 from FIG. 15E are patterned and etched to form thestructure shown in FIG. 15F. The gate dielectric after the etch processis indicated as 2424 while the gate electrode after the etch process isindicated as 2426. n+Si regions are indicated as 2418 while the glasssubstrate is indicated as 2402. Oxide regions 2404 and 2410 have beendescribed previously. It can be observed that a three-side gatedjunction-less transistor is formed at the end of the process describedwith respect of FIGS. 24A-F. Contacts, metallization and other steps forconstructing a display/microdisplay are performed after the stepsindicated by FIGS. 24A-F. It can be seen that the glass substrate is notexposed to temperatures greater than approximately 400° C. during anystep of the above process for forming the junction-less transistor.

FIGS. 25A-D describe an embodiment of this invention, where amorphous Sior polysilicon junction-less transistors are constructed above glasssubstrates at a temperature less than 400° C. This process could includeseveral steps that occur in a sequence from Step (A) to Step (D). Manyof these steps share common characteristics, features, modes ofoperation, etc. When identical reference numbers are used in differentdrawing figures, they are used to indicate analogous, similar oridentical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams-particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 16A. A glass substrate 2502 is taken anda layer of silicon oxide 2504 is deposited on the glass substrate 2502.Following this deposition, a layer of n+Si 2506 is deposited usinglow-pressure chemical vapor deposition (LPCVD) or plasma enhancedchemical vapor deposition (PECVD). This layer of n+Si could optionallybe hydrogenated. Step (B) is illustrated in FIG. 16B. A lithography andetch process is conducted to pattern the n+ Silicon layer 2506 in FIG.16A to form n+ Silicon regions 2518 in FIG. 16B. 2502 and 2504 have beendescribed previously. Step (C) is illustrated in FIG. 16C. A gatedielectric 2520 and gate electrode 2522 are deposited, following which aCMP is optionally done. 2502 is as described previously. The n+Siregions 2518 are not visible in this figure, since they are covered bythe gate electrode 2522.

Step (D) is illustrated in FIG. 16D. The gate dielectric 2520 and gateelectrode 2522 from FIG. 16C are patterned and etched to form thestructure shown in FIG. 16D. The gate dielectric after the etch processis indicated as 2524 while the gate electrode after the etch process isindicated as 2526. n+Si regions are indicated as 2518 while the glasssubstrate is indicated as 2502. It can be observed that a three-sidegated junction-less transistor is formed at the end of the processdescribed with respect of FIGS. 25A-D. Contacts, metallization and othersteps for constructing a display/microdisplay are performed after thesteps indicated by FIGS. 25A-D. It can be seen that the glass substrateis not exposed to temperatures greater than 400° C. during any step ofthe above process for forming the junction-less transistor.

FIGS. 26A-C illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare connected to each pixel with solder bumps. This process couldinclude several steps that occur in a sequence from Step (A) to Step(C). Many of these steps share common characteristics, features, modesof operation, etc. When identical reference numbers are used indifferent drawing figures, they are used to indicate analogous, similaror identical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams-particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 17A. Using procedures similar to FIG.4A-S, the structure shown in FIG. 17A is constructed. Various elementsof FIG. 17A are as follows:

-   -   2646—a glass substrate,    -   2644—an oxide layer, could be a conductive oxide such as ITO,    -   2634—an oxide layer, could be a conductive oxide such as ITO    -   2633—a an optional reflector, could be a Distributed Bragg        Reflector or some other type of reflector,    -   2632—a P-type confinement layer that is used for a Blue LED (One        example of a material for this region is GaN),    -   2630—a buffer layer that is typically used for a Blue LED (One        example of a material for this region is AlGaN),    -   2628—a multiple quantum well used for a Blue LED (One example of        materials for this region are InGaN/GaN),    -   2627—a N-type confinement layer that is used for a Blue LED (One        example of a material for this region is GaN).    -   2648—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2622—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2621—an optional reflector (for example, a Distributed Bragg        Reflector),    -   2620—a P-type confinement layer that is used for a Green LED        (One example of a material for this region is GaN),    -   2618—a buffer layer that is typically used for a Green LED (One        example of a material for this region is AlGaN),    -   2616—a multiple quantum well used for a Green LED (One example        of materials for this region are InGaN/GaN),    -   2615—a N-type confinement layer that is used for a Green LED        (One example of a material for this region is GaN),    -   2652—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2610—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2609—an optional reflector (for example, a Distributed Bragg        Reflector),    -   2608—a P-type confinement layer used for a Red LED (One example        of a material for this region is AlInGaP),    -   2606—a multiple quantum well used for a Red LED (One example of        materials for this region are AlInGaP/GaInP),    -   2604—a P-type confinement layer used for a Red LED (One example        of a material for this region is AlInGaP),    -   2656—an oxide layer, may be preferably a transparent conductive        metal oxide such as ITO, and    -   2658—a reflector (for example, aluminum or silver).

Step (B) is illustrated in FIG. 17B. Via holes 2662 are etched to thesubstrate layer 2646 to isolate different pixels in themicrodisplay/display. Also, via holes 2660 are etched to make contactsto various layers of the stack. These via holes may be preferably notfilled. An alternative is to fill the via holes with a compatible oxideand planarize the surface with CMP. Various elements in FIG. 17B such as2646, 2644, 2634, 2633, 2632, 2630, 2628, 2627, 2648, 2622, 2621, 2620,2618, 2616, 2 615, 2652, 2610, 2609, 2608, 2606, 2604, 2656 and 2658have been described previously. Step (C) is illustrated in FIG. 17C.Using procedures similar to those described in respect to FIGS. 4A-S,the via holes 2660 have contacts 2664 (for example, with Aluminum) madeto them. Also, using procedures similar to those described in FIGS.4A-S, nickel layers 2666, solder layers 2668, and a silicon sub-mount2670 with circuits integrated on them are constructed. The siliconsub-mount 2670 has transistors to control each pixel in themicrodisplay/display. Various elements in FIG. 17C such as 2646, 2644,2634, 2633, 2632, 2630, 2628, 2627, 2648, 2622, 2621, 2620, 2618, 2 616,2615, 2652, 2610, 2609, 2608, 2606, 2604, 2656, 2660, 2662, and 2658have been described previously.

It can be seen that the structure shown in FIG. 17C can have each pixelemit a certain color of light by tuning the voltage given to the red,green and blue layers within each pixel. This microdisplay may beconstructed using the ion-cut technology, a smart layer transfertechnique.

FIGS. 27A-D illustrate an embodiment of this invention, where amicrodisplay is constructed using stacked RGB LEDs and control circuitsare integrated with the RGB LED stack. This process could includeseveral steps that occur in a sequence from Step (A) to Step (D). Manyof these steps share common characteristics, features, modes ofoperation, etc. When identical reference numbers are used in differentdrawing figures, they are used to indicate analogous, similar oridentical structures to enhance the understanding of the presentinvention by clarifying the relationships between the structures andembodiments presented in the various diagrams-particularly in relatinganalogous, similar or identical functionality to different physicalstructures.

Step (A) is illustrated in FIG. 18A. Using procedures similar to thoseillustrated in FIGS. 4A-S, the structure shown in FIG. 18A isconstructed. Various elements of FIG. 18A are as follows:

-   -   2746—a glass substrate,    -   2744—an oxide layer, could be a conductive oxide such as ITO,    -   2734—an oxide layer, could be a conductive oxide such as ITO,    -   2733—a an optional reflector (e.g., a Distributed Bragg        Reflector or some other type of reflector),    -   2732—a P-type confinement layer that is used for a Blue LED (One        example of a material for this region is GaN),    -   2730—a buffer layer that is typically used for a Blue LED (One        example of a material for this region is AlGaN),    -   2728—a multiple quantum well used for a Blue LED (One example of        materials for this region are InGaN/GaN),    -   2727—a N-type confinement layer that is used for a Blue LED (One        example of a material for this region is GaN),    -   2748—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2722—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2721—an optional reflector (e.g., a Distributed Bragg        Reflector),    -   2720—a P-type confinement layer that is used for a Green LED        (One example of a material for this region is GaN),    -   2718—a buffer layer that is typically used for a Green LED (One        example of a material for this region is AlGaN),    -   2716—a multiple quantum well used for a Green LED (One example        of materials for this region are InGaN/GaN),    -   2715—a N-type confinement layer that is used for a Green LED        (One example of a material for this region is GaN),    -   2752—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2710—an oxide layer, may be preferably a conductive metal oxide        such as ITO,    -   2709—an optional reflector (e.g., a Distributed Bragg        Reflector),    -   2708—a P-type confinement layer used for a Red LED (One example        of a material for this region is AlInGaP),    -   2706—a multiple quantum well used for a Red LED (One example of        materials for this region are AlInGaP/GaInP),    -   2704—a P-type confinement layer used for a Red LED (One example        of a material for this region is AlInGaP),    -   2756—an oxide layer, may be preferably a transparent conductive        metal oxide such as ITO,    -   2758—a reflector (e.g., aluminum or silver).

Step (B) is illustrated in FIG. 18B. Via holes 2762 are etched to thesubstrate layer 2746 to isolate different pixels in themicrodisplay/display. Also, via holes 2760 are etched to make contactsto various layers of the stack. These via holes may be preferably filledwith a compatible oxide and the surface can be planarized with CMP.Various elements of FIG. 18B such as 2746, 2744, 2734, 2733, 2732, 2730,2728, 2727, 2748, 2722, 2721, 2720, 2718, 2716, 2715, 275 2, 2710, 2709,2708, 2706, 2704, 2756 and 2758 have been described previously. Step (C)is illustrated in FIG. 18C. Metal 2764 (for example) is constructedwithin the via holes 2760 using procedures similar to those described inrespect to FIGS. 4A-S. Following this construction, an oxide layer 2766is deposited. Various elements of FIG. 18C such as 2746, 2744, 2734,2733, 2732, 2730, 2728, 2727, 2748, 2722, 2721, 2720, 2718, 2716, 2715,2752, 2 710, 2709, 2708, 2706, 2704, 2756, 2760, 2762 and 2758 have beendescribed previously. Step (D) is illustrated in FIG. 18D. Usingprocedures described in co-pending U.S. patent application Ser. No.12/901,890, the content of which is incorporated herein by reference, asingle crystal silicon transistor layer 2768 can be monolithicallyintegrated using ion-cut technology atop the structure shown in FIG.18C. This transistor layer 2768 is connected to various contacts of thestacked LED layers (not shown in the figure for simplicity). Followingthis connection, nickel layer 2770 is constructed and solder layer 2772is constructed. The packaging process then is conducted where thestructure shown in FIG. 18D is connected to a silicon sub-mount. It canbe seen that the structure shown in FIG. 18D can have each pixel emit acertain color of light by tuning the voltage given to the red, green andblue layers within each pixel. This microdisplay is constructed usingthe ion-cut technology, a smart layer transfer technique. This processwhere transistors are integrated monolithically atop the stacked RGBdisplay can be applied to the LED concepts disclosed in association withFIGS. 4-10.

The embodiments of this invention described in FIGS. 26-27 may enablenovel implementations of “smart-lighting concepts” (also known asvisible light communications) that are described in “Switching LEDs onand off to enlighten wireless communications”, EETimes, June 2010 by R.Colin Johnson. For these prior art smart lighting concepts, LED lightscould be turned on and off faster than the eye can react, so signalingor communication of information with these LED lights is possible. Anembodiment of this invention involves designing thedisplays/microdisplays described in FIGS. 26-27 to transmit information,by modulating wavelength of each pixel and frequency of switching eachpixel on or off. One could thus transmit a high bandwidth through thevisible light communication link compared to a LED, since each pixelcould emit its own information stream, compared to just one informationstream for a standard LED. The stacked RGB LED embodiment described inFIGS. 4A-S could also provide a improved smart-light than prior artsince it allows wavelength tunability besides the ability to turn theLED on and off faster than the eye can react.

3-D Micro-Display

The three-dimensional (3D) display of images has been demonstrated bythe use of holography to the use of 3D glasses that use either color orpolarization. The main technique in common with these methods is toinduce stereoscopic vision by making each eye see a slightly offsetimage on the screen. Though effective in fooling the human brain intoseeing images in 3D, the problem with these techniques is that eventhough the desired effect can be achieved, the brain eventually isstrained, resulting in headaches for several individuals. FIG. 19Aillustrates the source of the straining of the brain. A system 3900 maybe set up such that the viewer 3902 is observing an object 3910projected on a display 3904. The source of the strain is from the factthat the actual image of the object 3910 is still a fixed distance onthe screen, while the image of the object perceived in the brain 3912can be within a few inches of the viewer 3902 or several miles away inperceived distance. As such, the eyes are focused on a screen severalfeet away while the brain perceives an image at a different location,and this separation of reality and image leads to brain and/or eyestrain.

In micro-displays, where the actual images are small but through the useof lenses are magnified to possibly life-size as interpreted by thebrain, this problem of eye/brain separation may also exist. Thedistances, however, are compressed by the magnification ratio of thelenses and thus the result is not as severe and is easier to rectify. Apossible solution is to move the display physically so as to show imagesaccording to their apparent distance from the viewer. If the objects attheir respective distances are shown in succession faster than the braincan perceive movement, then the brain will see all objects at variousapparent distances all at once, hence creating a total image containingall the object distance information, and will appear as an actual 3Dimage.

As the brain perceives distance in greater detail when close thanfarther away, the physical steps of the plane of the display may bearranged in nonlinear fashion, with more steps related to distancescloser to the viewer and less steps related to distances further away,that is, of increasing intervals as the distance grows larger with forexample, a geometric relationship.

Assuming enough 3D details of the objects in the image are available, anexternal joystick may also be used to control the vantage point of theimage or object/s to allow for virtual stage rotation.

FIG. 19B illustrates an embodiment of the invention, where a displaysystem 3920 may be set-up such that viewer 3922 observes an image whichmay consist of far object 3930 and near object 3932 projected onto thedisplay 3924. The display 3924 is enabled to physically move back andforth with respect to the viewer 3922 such that it may start from thefar end displaying only the far object 3930 and move forward to the nearend (nearer to viewer 3922) displaying only the near object 3932. Anyobjects that may be of intermediate distance from the viewer may then bedisplayed on the display 3924 during the sweep at their respectivedistances, but only one-at-a-time if the distances are distinct. Inorder to make the objects appear as one 3D image perceived by the brain,this forward and backward sweep of the display 3924 may be performed ata rate faster than about 24 cycles per second. If the image is intendedto show progression as in a movie, then the forward and backward sweepof the display 3924 may be performed at a rate faster than the framerate of the movie multiplied by 24 cycles per second. An actuator with afast motor which may be used to achieve such actuation speed mayinclude, for example, a piezo-electric motor (not shown).

FIG. 19C illustrates another embodiment of the invention, where adisplay system 3940 may be setup similar to display system 3920 in FIG.19B with viewer 3942 observing an image projected onto the movingdisplay 3944. The moving display 3944 may sweep forward and backwardwith respect to viewer 3942 similar to display system 3920 but the sweepsteps 3946 may not be of constant value but may be of nonlinearmagnitudes of the distance of the image objects. This takes advantage ofthe fact that the brain, by result of angular perception, recognizesdifferences in distances in greater detail when objects are closer andlesser detail when objects are further, so thus the display stepresolution for closer objects is necessarily dense but may beprogressively relaxed at greater object distances, such as shown byexemplary sweep steps 3946.

FIG. 19D illustrates another embodiment of the invention, where adisplay system 3960 may be setup similar to display system 3920 in FIG.19B with viewer 3962 observing an image object 3970 projected onto themoving display 3964. Computer 3968 may contain 3D data of image object3970 available for display and may be connected via link 3972 to thedisplay 3964. Computer 3968 may also be connected via link 3974 tojoystick 3966, which allows viewer 3962 to control the orientation ofthe image object 3970 according to available 3D data stored in computer3968.

Persons of ordinary skill in the art will appreciate that while image“objects” has been referred to as display targets, these mayequivalently be replaced by the term image “pixels”. Moreover, thenonlinear steps of the display forward-backward sweep described in FIG.39 FIG. 19C may be of any resolution and may involve any type ofnonlinear relationships with viewer distance as desired. Many othermodifications within the scope of the illustrated embodiments of theinvention will suggest themselves to such skilled persons after readingthis specification. Thus the invention is to be limited only by theappended claims Persons of ordinary skill in the art will appreciatethat while image “objects” has been referred to as display targets,these may equivalently be replaced by the term image “pixels”. Moreover,the nonlinear steps of the display forward-backward sweep described inFIG. 19C may be of any resolution and may involve any type of nonlinearrelationships with viewer distance as desired.

Many other modifications within the scope of the illustrated embodimentsof the invention will suggest themselves to such skilled persons afterreading this specification. Thus the invention is to be limited only bythe appended claims

We claim:
 1. A 3D micro display, the 3D micro display comprising: afirst level comprising a first single crystal layer, said first singlecrystal layer comprises at least one LED driving circuit; a second levelcomprising a first plurality of light emitting diodes (LEDs), said firstplurality of LEDs comprising a second single crystal layer, wherein saidsecond level is disposed on top of said first level, wherein said secondlevel comprises at least ten individual first LED pixels; and a bondingstructure, wherein said bonding structure comprises oxide to oxidebonding.
 2. The 3D micro display according to claim 1, wherein aplurality of said at least ten individual first LED pixels areindividually driven, and wherein each of said plurality of said at leastten individual first LED pixels is driven by a unique said at least oneLED driving circuit.
 3. The 3D micro display according to claim 1,further comprising: a top surface of said first single crystal layer;and a bottom surface of said second single crystal layer, wherein avertical distance is a distance from said top surface of said firstsingle crystal layer to said bottom surface of said second singlecrystal layer, and wherein said vertical distance is less than tenmicrons and greater than 0.1 microns.
 4. The 3D micro display accordingto claim 1, further comprising: a second plurality of light emittingdiodes (LEDs), wherein said first plurality of LEDs emits a first lightwith a first wavelength, wherein said second plurality of LEDs emits asecond light with a second wavelength, and wherein said first wavelengthand said second wavelength differ by greater than 10 nm.
 5. The 3D microdisplay according to claim 1, wherein said first single crystal layerthickness is greater than 10 nm and smaller than 50 micrometers.
 6. The3D micro display according to claim 1, wherein said second singlecrystal layer thickness is greater than 10 nm and smaller than 50micrometers.
 7. The 3D micro display according to claim 1, wherein saidat least one LED driving circuit comprises n type devices and p typedevices.
 8. A 3D micro display, the 3D micro display comprising: a firstlevel comprising a first single crystal layer, said first single crystallayer comprises at least one LED driving circuit; a second levelcomprising a first plurality of light emitting diodes (LEDs), said firstplurality of LEDs comprising a second single crystal layer, wherein saidsecond level is disposed on top of said first level, wherein said secondlevel comprises at least ten individual first LED pixels; and a bondingstructure, wherein said first level is bonded to said second level, andwherein said bonded comprises oxide to oxide bonding.
 9. The 3D microdisplay according to claim 8, wherein a plurality of said at least tenindividual first LED pixels are individually driven, and wherein each ofsaid plurality of said at least ten individual first LED pixels isdriven by a unique said at least one LED driving circuit.
 10. The 3Dmicro display according to claim 8, further comprising: a top surface ofsaid first single crystal layer; and a bottom surface of said secondsingle crystal layer, wherein a vertical distance is a distance fromsaid top surface of said first single crystal layer to said bottomsurface of said second single crystal layer, and wherein said verticaldistance is less than ten microns and greater than 0.1 microns.
 11. The3D micro display according to claim 8, further comprising: a secondplurality of light emitting diodes (LEDs), wherein said first pluralityof LEDs emits a first light with a first wavelength, wherein said secondplurality of LEDs emits a second light with a second wavelength, andwherein said first wavelength and said second wavelength differ bygreater than 10 nm.
 12. The 3D micro display according to claim 8,wherein said first single crystal layer thickness is greater than 10 nmand smaller than 50 micrometers.
 13. The 3D micro display according toclaim 8, wherein said second single crystal layer thickness is greaterthan 10 nm and smaller than 50 micrometers.
 14. The 3D micro displayaccording to claim 8, wherein said at least one LED driving circuitcomprises n type devices and p type devices.
 15. A 3D micro display, the3D micro display comprising: a first level comprising a first singlecrystal layer, said first single crystal layer comprises at least oneLED driving circuit; a second level comprising a first plurality oflight emitting diodes (LEDs), said first plurality of LEDs comprising asecond single crystal layer, wherein said second level is disposed ontop of said first level, wherein said second level comprises at leastten individual first LED pixels, wherein said first plurality of LEDscomprise at least 10 individual LED pixels, wherein said at least 10individual LED pixels been made individual by an etch process; and abonding structure, wherein said first level is bonded to said secondlevel, and wherein said bonded comprises oxide to oxide bonding.
 16. The3D micro display according to claim 15, wherein a plurality of saidfirst LED pixels are individually driven, and wherein each of saidplurality of said first LED pixels is driven by a unique said at leastone LED driving circuit.
 17. The 3D micro display according to claim 15,further comprising: a top surface of said first single crystal layer;and a bottom surface of said second single crystal layer, wherein avertical distance is a distance from said top surface of said firstsingle crystal layer to said bottom surface of said second singlecrystal layer, and wherein said vertical distance is less than tenmicrons and greater than 0.1 microns.
 18. The 3D micro display accordingto claim 15, further comprising: a second plurality of light emittingdiodes (LEDs), wherein said first plurality of LEDs emits a first lightwith a first wavelength, wherein said second plurality of LEDs emits asecond light with a second wavelength, and wherein said first wavelengthand said second wavelength differ by greater than 10 nm.
 19. The 3Dmicro display according to claim 15, wherein said first single crystallayer thickness is greater than 10 nm and smaller than 50 micrometers.20. The 3D micro display according to claim 15, wherein said at leastone LED driving circuit comprises n type devices and p type devices.